Abnormal meiotic chromosome behavior and gametic variation induced by intersectional hybridization in Populus L.

Abstract

Abnormal meiotic chromosome behavior and pollen variation in two intersectional hybrids between Populus simonii Carr. (section Tacamahaca Spach) and Populus euphratica Oliv. (section Turanga Bge.) were investigated by the squashed technique and indirect immunofluorescence. Both hybrids produced abnormal flower buds characterized by a primary bud with an accessary bud at frequencies of 39.0 and 17.8 %, respectively. Chromosome pairing analysis at late diakinesis showed average configurations 20.31 I + 7.04 II + 1.42 III + 0.04 IV in hybrid “Xhu-DK” and 19.18 I + 7.16 II + 1.45 III + 0.04 IV in hybrid “Xhu-TL”, indicating high divergence between their parent species. Meiotic abnormalities, including precocious chromosome migration, lagging chromosomes, chromosome bridges, and micronuclei, were observed at high frequency, resulting in imbalanced chromosome segregation and chromosome elimination and caused high gamete sterility. Some micronuclei triggered formation of minispindles in Metaphase II, which were responsible for the formation of microcytes. Fused and tripolar spindles in the second meiotic division developed into dyads and triads, respectively, leading to viable first meiotic division restitution (FDR) type unreduced pollen formation. However, Xhu-TL was completely sterile because the high frequency of precocious cytokinesis during the second division prevented unreduced pollen formation though spindle fusion. Xhu-DK produced 29.6 % viable pollen grains. The diameter of viable pollen ranged from 19.6 to 64.9 μm, suggesting that Xhu-DK might be capable of producing unreduced pollen or pollen with a higher ploidy level. The strategy of using the distant hybrids for chromosome introgression and polyploidy breeding in Populus L. was considered.